I provided as much context as I can below, but looking for recommendations on addressing new fear reactivity towards other humans while my dog is in his adolescent fear period. At the very least, I just don't want to be making things worse before we get started with a trainer in a couple weeks.
My pup is coming up on 10 months old, we adopted him around 3.5 months old. He came from the rescue already neutered, with severe giardia and coronavirus, he had not been properly vaccinated, and was only partially potty trained to pee pads. Not a great start for him, so our first two months with him were just potty training, and getting him healthy.
We did a wisdom panel on him and he's husky, malamute, gsd, staffy, pit, and a handful of other breeds in small percentages. He's mostly husky, looks like a white/cream husky but with short hair and he's plateaued at 45lbs right now. He's a high energy and very intelligent dog.
We live in an urban environment in a condo, so he gets lots of play time at home, puzzle feeders, and 4+ miles of walking per day. A few days a week he walks to work with me and spends the day in my corporate office with me, where he sees 40+ people and interacts with 5+ people who regularly come into my office to talk to me. The rest of the time he's at home with my partner who works from home, so he's always with us or rarely left by himself for a half day, he doesn't go to doggy care or anywhere that he's exposed to humans and dogs without us.
When we adopted him, he was very out going with humans and very reactive to other dogs, but in a very "I want to play" way, like jumping/lunging and getting into a play bow stance, tail wagging, like definitely reactive, but not from a place of fear. We've made so much progress in this area, we are able to walk by most dogs with very little or no reaction. The only time we still have an issue is when it's a dog that's going nuts reacting to him, usually a small dog barking and lunging at him. We're making progress with that too though, and I feel confident we're not far from fully getting through this reactivity.
Around 7 months old he started being more cautious about meeting people, but as long as the environment was calm and he got a chance to approach on his own, he was still willing to meet people. Around 8 months old, that dropped off and he no longer wants to meet any one, and is now even nervous about people he's known for several months. In the last ~6 weeks this has escalated very quickly and has gotten to the point where he is growling at people who are waiting to get on the elevator when we are getting off, and trying to bolt when people pass by too close to us on the sidewalk when we're out on our walks. Hes also been getting super startled by random loud city noises. None of these things used to bother him at all, he's been exposed to all of these things since we got him, but now it's a very clear fear reaction.
I've come to understand that he's in his second fear period, and I'm at a loss on how to handle this because nothing about our routines have really changed, he has been exposed to all these environmental factors / people his whole life with us, but his fear is escalating so quickly, I am terrified if we don't get ahead of it now we're going to have a long life of this reactivity.